As is known, helicopters are normally equipped with a number of transmissions for transmitting motion from one or more turbines to the main and/or tail rotor, and/or from the turbine to a number of accessory devices, i.e. for powering on-board equipment, for example.
The transmissions normally comprise a first member movable with respect to a second member; and a number of bearings for supporting the first member with respect to the second member. Helicopters also comprise a circuit for supplying and lubricating the bearings with lubricating oil contained inside special tanks.
In the event of damage to the lubricating circuit, the oil pressure falls, thus preventing operation of the transmission.
In the industry, a need is felt to ensure, in such cases, correct operation of the transmission for a predetermined length of time, e.g. at least thirty minutes and preferably an hour, to allow the helicopter to land.
Moreover, for missions of a given duration, helicopter certification regulations require that the helicopter be able to maintain level flight for said predetermined length of time.